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[dev.typeparams] cmd/compile/internal/types2: a type parameter is a valid type case in a type switch

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Likewise for type assertions.

This is a port of https://golang.org/cl/273127 to dev.typeparams.

Updates #42758.

Change-Id: If93246371c3555e067b0043f0caefaac99101ebc
Reviewed-on: https://go-review.googlesource.com/c/go/+/273128
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
This commit is contained in:
Robert Griesemer 2020-11-24 22:07:04 -08:00
parent 0fb733b7f7
commit 2c25cd5ba7
3 changed files with 43 additions and 27 deletions
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20
src/cmd/compile/internal/types2/expr.go
View File

@ -1703,22 +1703,12 @@ func (check *Checker) exprInternal(x *operand, e syntax.Expr, hint Type) exprKin
if x.mode == invalid {
goto Error
}
var xtyp *Interface
var strict bool
switch t := optype(x.typ.Under()).(type) {
case *Interface:
xtyp = t
// Disabled for now. It is not clear what the right approach is
// here. Also, the implementation below is inconsistent because
// the underlying type of a type parameter is either itself or
// a sum type if the corresponding type bound contains a type list.
// case *TypeParam:
// xtyp = t.Bound()
// strict = true
default:
check.invalidOpf(x, "%s is not an interface type", x)
xtyp, _ := x.typ.Under().(*Interface)
if xtyp == nil {
check.errorf(x, "%s is not an interface type", x)
goto Error
}
check.ordinaryType(x.Pos(), xtyp)
// x.(type) expressions are encoded via TypeSwitchGuards
if e.Type == nil {
check.invalidASTf(e, "invalid use of AssertExpr")
@ -1728,7 +1718,7 @@ func (check *Checker) exprInternal(x *operand, e syntax.Expr, hint Type) exprKin
if T == Typ[Invalid] {
goto Error
}
check.typeAssertion(posFor(x), x, xtyp, T, strict)
check.typeAssertion(posFor(x), x, xtyp, T, false)
x.mode = commaok
x.typ = T

33
src/cmd/compile/internal/types2/fixedbugs/issue42758.go2 Normal file
View File

@ -0,0 +1,33 @@
// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package p
func _[T any](x interface{}){
switch x.(type) {
case T: // ok to use a type parameter
case int:
}
switch x.(type) {
case T:
case T /* ERROR duplicate case */ :
}
}
type constraint interface {
type int
}
func _[T constraint](x interface{}){
switch x.(type) {
case T: // ok to use a type parameter even if type list contains int
case int:
}
}
func _(x constraint /* ERROR contains type constraints */ ) {
switch x /* ERROR contains type constraints */ .(type) {
}
}

17
src/cmd/compile/internal/types2/stmt.go
View File

@ -666,19 +666,12 @@ func (check *Checker) typeSwitchStmt(inner stmtContext, s *syntax.SwitchStmt, gu
if x.mode == invalid {
return
}
var xtyp *Interface
var strict bool
switch t := x.typ.Under().(type) {
case *Interface:
xtyp = t
// Disabled for now. See comment in the implementation of type assertions (expr.go).
// case *TypeParam:
// xtyp = t.Bound()
// strict = true
default:
check.errorf(&x, "%s is not an interface or generic type", &x)
xtyp, _ := x.typ.Under().(*Interface)
if xtyp == nil {
check.errorf(&x, "%s is not an interface type", &x)
return
}
check.ordinaryType(x.Pos(), xtyp)
check.multipleSwitchDefaults(s.Body)
@ -691,7 +684,7 @@ func (check *Checker) typeSwitchStmt(inner stmtContext, s *syntax.SwitchStmt, gu
}
// Check each type in this type switch case.
cases := unpackExpr(clause.Cases)
T := check.caseTypes(&x, xtyp, cases, seen, strict)
T := check.caseTypes(&x, xtyp, cases, seen, false)
check.openScope(clause, "case")
// If lhs exists, declare a corresponding variable in the case-local scope.
if lhs != nil {